[单项选择]
Plant Gas
Scientists have been studying natural sources of methane for decades but hadn’t regarded plants as a producer, notes Frank Keppler, a geochemist at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Now Keppler and his colleagues find that plants, from grasses to trees, may also be sources of the greenhouse gas. This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously, researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes need to be in environments without oxygen to produce methane. Methane is a greenhouse gas, like carbon dioxide. Gases such as methane and carbon dioxide trap heat in Earth’s atmosphere and contribute to global warming.
In its experiments, Keppler’s team used sealed chambers that contained the same concentration of oxygen that Earth’s atm
A. It was produced from plants.
B. It was not a greenhouse gas.
C. It was produced in oxygen-free environments.
D. It traps more heat than any other greenhouse gas.